Electrically conducting polymers having a sulfonic acid group or a carboxyl group are expected to exhibit an excellent solubility in water and organic solvents, so that various synthesis methods have been studied. Also, there have been reported methods for forming electric conductors comprising these electrically conductive polymers as the main component, and the like (JP-A-61-197633, JP-A-63-39916, JP-A-01-301714, JP-A-05-504153, JP-A-05-503953, JP-A-04-32848, JP-A-04-328181, JP-A-06-145386, JP-A-06-56987, JP-A-05226238, JP-A-05-178989, JP-A-06-293828, JP-A-07-118524, JP-A-0682845, JP-A-06-87949, JP-A-06-256516, JP-A-07-41756, JP-A-07-48436 and JP-A-04-268331).
However, since these soluble, electrically conducting polymers are excellent in solubility in water and organic solvents, there is such a disadvantage that electrically conductive films composed of these polymers are rather inferior in water resistance and solvent resistance. The purpose of this invention is to enhance the water resistance and solvent resistance of an electrically conducive film composed of a soluble, electrically conducting polymer having a sulfonic acid group or a carboxyl group.
As a method for the anticorrosion of the surface of a metal, a method of coating the metal surface has been generally adopted. A method of coating the metal surface with a high molecular weight compound has such a disadvantage that corrosion proceeds from the defect portion of the coating film. Moreover, a method of coating the metal surface with a chromic acid compound exhibits a very excellent anticorrosive effect; however, a substitutive method has been required from the viewpoint of both environment and health. Furthermore, a method of controlling the potential of a metal to a constant value exerts an excellent effect; however, an outside electric source and a means for controlling the potential become necessary and hence the application thereof is, as a matter of course, limited technically and economically.
Therefore, an anticorrosion method which comprises coating the metal surface with an electrically conductive polymer to control the potential to a constant value has been proposed. For example, a method which comprises coating the metal surface with a polyaniline as an electrically conductive polymer by electrolysis polymerization has been proposed [J. Electrochim. Soc., 132, 1022 (1988)]; however, it is difficult to apply this method to a metal surface having a large surface area.
Furthermore, a method which comprises coating the metal surface with a powdery polyaniline dispersed in a high molecular weight compound (JP-A-63-199884) has also been proposed; however, the anticorrosive effect is insufficient because the dispersion is not uniform.
A method which comprises dissolving a polyaniline in the dedoped state in a polar, organic solvent such as N-methylpyrrolidone or the like (JP-A-03-28229) has been proposed. However, a step of doping with a protonic acid is required after the coating, and hence, the above method is inappropriate in industry.
A method which comprises dissolving a polyaniline in the doped state in a polar, organic solvent by adding an amine such as ammonia or the like (JP-A-03-285983) has also been proposed. However, this method cannot be used in industry because ammonia is volatilized during drying. A method which comprises coating the metal surface with a solution of a soluble polyaniline and a dopant in an organic solvent (JP-A-5-320958) has been proposed; however, this method has a problem in that the addition of a dopant is necessary, and hence, the method is industrially complicated and that the solubility of the polyaniline is not sufficient. Moreover, since the polyaniline is insoluble in water, only an organic solvent must be used and this is not desirable in view of global environmental problems.
A method which comprises solubilizing a polyaniline in the doped state (JP-A-08-92479) has been proposed; however, this has a problem in industrial application because the solubility and the stability of solution are not sufficient.
Thus, in the present technical field, the development of an anticorrosive composition which, when used in the anticorrosion of a metal, is soluble in both water and organic solvents, can easily be applied to and coated on the metal, and can form a very thin film which can exert sufficient anticorrosion performance, has become an important problem.
This invention has been made for the purpose of overcoming the disadvantages possessed by conventional anticorrosive agents as mentioned above and providing an anticorrosive composition which is soluble in both water and organic solvents, is excellent in metal-applicability and metal-coatability and can exert sufficient anticorrosion performance, and also providing an anticorrosion method using the above corrosive composition.